#include "crc32.h"

unsigned int crctab[] = {
      0x00000000,  0x04c11db7,  0x09823b6e,  0x0d4326d9,
      0x130476dc,  0x17c56b6b,  0x1a864db2,  0x1e475005,
      0x2608edb8,  0x22c9f00f,  0x2f8ad6d6,  0x2b4bcb61,
      0x350c9b64,  0x31cd86d3,  0x3c8ea00a,  0x384fbdbd,
      0x4c11db70,  0x48d0c6c7,  0x4593e01e,  0x4152fda9,
      0x5f15adac,  0x5bd4b01b,  0x569796c2,  0x52568b75,
      0x6a1936c8,  0x6ed82b7f,  0x639b0da6,  0x675a1011,
      0x791d4014,  0x7ddc5da3,  0x709f7b7a,  0x745e66cd,
      0x9823b6e0,  0x9ce2ab57,  0x91a18d8e,  0x95609039,
      0x8b27c03c,  0x8fe6dd8b,  0x82a5fb52,  0x8664e6e5,
      0xbe2b5b58,  0xbaea46ef,  0xb7a96036,  0xb3687d81,
      0xad2f2d84,  0xa9ee3033,  0xa4ad16ea,  0xa06c0b5d,
      0xd4326d90,  0xd0f37027,  0xddb056fe,  0xd9714b49,
      0xc7361b4c,  0xc3f706fb,  0xceb42022,  0xca753d95,
      0xf23a8028,  0xf6fb9d9f,  0xfbb8bb46,  0xff79a6f1,
      0xe13ef6f4,  0xe5ffeb43,  0xe8bccd9a,  0xec7dd02d,
      0x34867077,  0x30476dc0,  0x3d044b19,  0x39c556ae,
      0x278206ab,  0x23431b1c,  0x2e003dc5,  0x2ac12072,
      0x128e9dcf,  0x164f8078,  0x1b0ca6a1,  0x1fcdbb16,
      0x018aeb13,  0x054bf6a4,  0x0808d07d,  0x0cc9cdca,
      0x7897ab07,  0x7c56b6b0,  0x71159069,  0x75d48dde,
      0x6b93dddb,  0x6f52c06c,  0x6211e6b5,  0x66d0fb02,
      0x5e9f46bf,  0x5a5e5b08,  0x571d7dd1,  0x53dc6066,
      0x4d9b3063,  0x495a2dd4,  0x44190b0d,  0x40d816ba,
      0xaca5c697,  0xa864db20,  0xa527fdf9,  0xa1e6e04e,
      0xbfa1b04b,  0xbb60adfc,  0xb6238b25,  0xb2e29692,
      0x8aad2b2f,  0x8e6c3698,  0x832f1041,  0x87ee0df6,
      0x99a95df3,  0x9d684044,  0x902b669d,  0x94ea7b2a,
      0xe0b41de7,  0xe4750050,  0xe9362689,  0xedf73b3e,
      0xf3b06b3b,  0xf771768c,  0xfa325055,  0xfef34de2,
      0xc6bcf05f,  0xc27dede8,  0xcf3ecb31,  0xcbffd686,
      0xd5b88683,  0xd1799b34,  0xdc3abded,  0xd8fba05a,
      0x690ce0ee,  0x6dcdfd59,  0x608edb80,  0x644fc637,
      0x7a089632,  0x7ec98b85,  0x738aad5c,  0x774bb0eb,
      0x4f040d56,  0x4bc510e1,  0x46863638,  0x42472b8f,
      0x5c007b8a,  0x58c1663d,  0x558240e4,  0x51435d53,
      0x251d3b9e,  0x21dc2629,  0x2c9f00f0,  0x285e1d47,
      0x36194d42,  0x32d850f5,  0x3f9b762c,  0x3b5a6b9b,
      0x0315d626,  0x07d4cb91,  0x0a97ed48,  0x0e56f0ff,
      0x1011a0fa,  0x14d0bd4d,  0x19939b94,  0x1d528623,
      0xf12f560e,  0xf5ee4bb9,  0xf8ad6d60,  0xfc6c70d7,
      0xe22b20d2,  0xe6ea3d65,  0xeba91bbc,  0xef68060b,
      0xd727bbb6,  0xd3e6a601,  0xdea580d8,  0xda649d6f,
      0xc423cd6a,  0xc0e2d0dd,  0xcda1f604,  0xc960ebb3,
      0xbd3e8d7e,  0xb9ff90c9,  0xb4bcb610,  0xb07daba7,
      0xae3afba2,  0xaafbe615,  0xa7b8c0cc,  0xa379dd7b,
      0x9b3660c6,  0x9ff77d71,  0x92b45ba8,  0x9675461f,
      0x8832161a,  0x8cf30bad,  0x81b02d74,  0x857130c3,
      0x5d8a9099,  0x594b8d2e,  0x5408abf7,  0x50c9b640,
      0x4e8ee645,  0x4a4ffbf2,  0x470cdd2b,  0x43cdc09c,
      0x7b827d21,  0x7f436096,  0x7200464f,  0x76c15bf8,
      0x68860bfd,  0x6c47164a,  0x61043093,  0x65c52d24,
      0x119b4be9,  0x155a565e,  0x18197087,  0x1cd86d30,
      0x029f3d35,  0x065e2082,  0x0b1d065b,  0x0fdc1bec,
      0x3793a651,  0x3352bbe6,  0x3e119d3f,  0x3ad08088,
      0x2497d08d,  0x2056cd3a,  0x2d15ebe3,  0x29d4f654,
      0xc5a92679,  0xc1683bce,  0xcc2b1d17,  0xc8ea00a0,
      0xd6ad50a5,  0xd26c4d12,  0xdf2f6bcb,  0xdbee767c,
      0xe3a1cbc1,  0xe760d676,  0xea23f0af,  0xeee2ed18,
      0xf0a5bd1d,  0xf464a0aa,  0xf9278673,  0xfde69bc4,
      0x89b8fd09,  0x8d79e0be,  0x803ac667,  0x84fbdbd0,
      0x9abc8bd5,  0x9e7d9662,  0x933eb0bb,  0x97ffad0c,
      0xafb010b1,  0xab710d06,  0xa6322bdf,  0xa2f33668,
      0xbcb4666d,  0xb8757bda,  0xb5365d03,  0xb1f740b4
};

unsigned int crc32_initial(unsigned char *data, int len)
{
    unsigned int        result = 0;
    int                 i;
    
    if (len < 4) {
      switch (len) {
      case 3:
        result = result << 8 | *data++;
      case 2:
        result = result << 8 | *data++;
      case 1:
        result = result << 8 | *data++;
      }
      return result;
    }

    result = *data++ << 24;
    result |= *data++ << 16;
    result |= *data++ << 8;
    result |= *data++;
    result = ~ result;
    len -=4;
    
    for (i=0; i<len; i++)
    {
        result = (result << 8 | *data++) ^ crctab[result >> 24];
    }
    
    return ~result;
}

unsigned int crc32_update(unsigned char *data, int len, unsigned int previous) {
  unsigned int result = ~ previous;
  int i;
  
  for (i=0; i<len; i++) {
    result = (result << 8 | *data++) ^ crctab[result >> 24];
  }
  
  return ~result;
}

static unsigned char checksum3[4] = {0, 0, 0, 0xFF};
static unsigned char checksum_array[7] = {0xFF, 0xFF, 0xFF, 0, 0, 0, 0};

unsigned int checksum_update(unsigned char *data, int len, unsigned int previous) {
  unsigned int result = previous;
  int i;
  unsigned int *ptr = (unsigned int *)data;
  int size = len >> 2;
  for (i=0; i<size; ++i) result ^= *ptr++;
  result ^= *ptr & *(unsigned int*)&(checksum_array[3-(len&3)]);
  return result;
}

unsigned int checksum_initial(unsigned char *data, int len) {
  return checksum_update(data, len, 0);
}
